1. Field of the Invention
The present invention relates to a display technology provided with OSD (on-screen display) function, more specifically, to a technology for preventing the jumping phenomenon of the OSD display region on the monitor screen, which is frequently caused by the adjustment operation for adjusting display parameters, such as adjusting the H-phase (horizontal phase in the screen).
2. Description of the Related Art
Display devices (include TV, monitors of the computer, etc.) usually provide some tunable parameters for users to adjust some display features during practical operation. For example, H-size/V-size parameters are used to tune the size feature of the display screen and H-phase/V-phase parameters are used to tune the position feature of the display screen. PWM (pulse width modulation) waveforms are generally employed to transfer these displaying parameters set by the user to corresponding deflection circuits, thereby adjusting the practical appearance of the display screen. Thus, display devices can provide an operational mechanism for the users to readily adjust these displaying parameters.
There are two approaches to adjusting these displaying parameters by the users in the modern display devices. The first one is to adjust these display parameters by the LEDs (light-emitted diodes) and the keys mounted on the control panel of the display device. When a user selects one of these parameter by using a select key, an LED corresponding to the selected parameter is lit up to announce the selection result. At this time, the user can practically press an adjust key to adjust the value of the selected display parameter. The second one is to adjust the displaying parameters by using the OSD display and the keys. The difference between the two approaches is the indication manner for indicating operation information. When a user touches the select key on the panel, the OSD menu is activated and displayed. Therefore, a display region showing the OSD menu will appear on a certain screen location, indicating the information of various displaying parameters, respectively. Thus the user can select a displaying parameter that needs to be adjusted by depressing the select key. In fact, the two approaches described above are almost the same, except for the manner of displaying the operation information. Owing to the requirement of a great number of LEDs in the first approach and the superior display effect provided by the second approach, most of the modern display devices adopt the OSD menu to illustrate the operation information.
FIG. 1 is a block diagram of the image-processing circuit in the conventional monitor with OSD function. Referring to FIG. 1, R(red), G(green) and B(blue) are three image signals transmitted from a video card, which represent the information of the three primary color data, red, green and blue, respectively. In the normal display condition, the image signals R, G and B are processed by a mixer circuit 8 and a amplifier 10 and finally transmitted to a picture tube 2 of the CRT(cathode ray tube) for displaying the image. Meanwhile, a deflection circuit 4 can control the displaying feature for this image according to timing signals, such as horizontal synchronizing signal Hs and vertical synchronizing signal Vs. The synchronizing signals Hs and Vs look like pulsed signals having a plurality of pulses. The pulse width in the horizontal synchronizing signal Hs is generally narrower than that in the vertical synchronizing signal Vs. The horizontal synchronizing signal Hs is used to define horizontal scanning lines, and the vertical synchronizing signal Vs is used to define picture fields or frames, each of which comprises a great number of scanning lines. Then the image represented by the image signals R, G and B can be properly displayed on the screen under the control of the deflection circuit 4.
When a user activates the OSD display function, a microprocessor (not shown) in the display device will read out the letter image information ready to be displayed from an EEPPOM (not shown), and transmit it to an OSD circuit 6 for producing OSD image signals Rosd, Gosd and Bosd corresponding to the three primary colors. The OSD circuit 6 sends the OSD image signals (Rosd, Gosd, Bosd) and a blanking signal BLK to the mixer circuit 8. The blanking signal BLK is used to define an OSD display region on the display screen. When the blanking signal BLK=1, it represents that the currently scanning spot in the screen is the normal image region. Then the mixer circuit 8 can block the OSD image signals Rosd, Gosd and Bosd, and passes the normal image signals R, G and B to the amplifier 10. On the contrary, When the blanking signal BLK=0, it represents that the currently scanning spot in the screen is the OSD display region. Then the mixer circuit 8 can block the normal image signals R, G and B, and pass the OSD image signals Rosd, Gosd and Bosd to the amplifier 10.
The blanking signal BLK is determined by the relative timing relation between the synchronizing signals Hs and Vs, that is, by deciding the range of the scanning lines for the OSD display region. Assume that the OSD display region starts at the 240.sup.th scanning line of the monitor screen, and totally occupies 120 scanning lines. Therefore, the OSD processing circuit begins to count the number of the scanning line when the vertical synchronizing signal indicates the top of the picture frame, outputs the blanking signal BLK=0 while counting the 240.sup.th scanning line, and output the blanking signal BLK=1 while counting the 360.sup.th scanning line.
According to the above-indicated description, the OSD display region can be determined by the synchronizing signals Hs and Vs, so the relation between the synchronizing signals Hs and Vs may affect the displaying of the OSD menu. The problem is that some adjusting operation for the display parameters, such as H-phase display parameter adjustment, may immediately affect the relative timing between the synchronizing signals Hs and Vs in the modern monitors. FIG. 2 and FIG. 3 illustrate the timing relation between the synchronizing signals Hs and Vs, before and after the adjustment of H-phase parameter in the prior art, for explaining the relative variation of the synchronizing signals Vs and Hs.
As the timing diagram shown in FIG. 2, before the adjustment operation, the front edge of a pulse of Vs (denoted by Ta) leads the front edge of a pulse of Hs (denoted by Tb), that is, Tb&gt;Ta. In addition, the front edges of the synchronizing signals Hs and Vs are relatively close.
Since the two edges are quite close, it is possible that the timing relationship between the synchronizing signals Hs and Vs is changed when the user adjusts the H-phase parameter. Suppose that the timing relation between the synchronizing signals Hs and Vs is changed to the situation shown in FIG. 3 by applying a certain amount of H-phase adjustment. In the situation shown in FIG. 3, the front edge of the horizontal synchronizing signal Hs (denoted by Ta') leads the front edge of the vertical synchronizing signal Vs (denoted by Tb').
As described above, the OSD processing circuit decides how to transmit the blanking signal BLK according to the relative relation between the synchronizing signals Hs and Vs. Therefore, if during the adjustment of the H-phase parameter, the relation between the synchronizing signals Vs and Hs is changed from the case of "the edge of pulse of Vs leading" to "the edge of pulse of Hs leading", the OSD processing circuit might not correctly count the number of the scanning lines. Usually, there is a miss of one scanning line in counting. Such a miss may make the jumping of the OSD display region happen. This is a shortcoming of the prior art monitors having the OSD function.
One proposed method to solve this problem is implemented by using the technique of signal delaying. If some timing situations that may induce the jumping phenomenon of the OSD display region are known, the synchronizing signals Hs will be in advance delayed at a predetermined time to avoid the happening of the variation of the timing relation between the synchronizing signals Hs and Vs due to the adjustment of the H-phase parameter. However, this method can only solve the jumping problem in some known situations, and cannot be generally applied to all situations.